In general, thiacarbocyanines and selenacarbocyanines have been used as sensitizing dyes for the red-sensitivity of silver halide color light-sensitive materials (hereinafter sometimes referred to as "color light-sensitive materials"). The use of such sensitizing dyes in combination results in the production of color light-sensitive materials having increased sensitivity to red light.
These sensitizing dyes, however, have disadvantages in that color reproduction of red and green is poor because they have a broad spectral sensitivity distribution and are somewhat sensitive to green light.
Thiacarbocyanine is strongly adsorbed on silver halide, giving rise to problems in that it decreases the intrinsic sensitivity of silver halide and tends to inhibit an increase in sensitivity during the processing of development, particularly at the stage of pushed development generally called "sensitizing treatment".
The absorption peak of spectral sensitization of a system in which the foregoing sensitizing dyes are used in combination is in the region of 655 to 660 nm, which is longer than that for the preferred absorption peak of spectral sensitization. From a viewpoint of color reproduction, therefore, it has been desired to discover sensitizing dyes producing the absorption peak in a region which is 5 to 10 nm shorter than the foregoing region.
However, when the chemical structure of the spectral sensitizing dye is slightly changed in order to shift the absorption peak of spectral sensitization to the preferred region by only about 5 to 10 nm, various problems are often involved, including a serious change in sensitivity, changes in rate of development, and adverse influences on storage properties.
The use of thiacarbocyanine or selenacarbocyanine in combination with holopolar cyanine is known as described in, for example, U.S. Pat. Nos. 2,704,718 and 3,547,623. However, even if they are used in combination with each other, no sufficient sensitivity can be obtained and color reproduction in the red-sensitive region is insufficient.